<p>Dietary protein quantity and quality may influence metabolic regulation and cardio-metabolic outcomes, yet little is known about their role in metabolic syndrome (MetS) reversion, a beneficial transition linked to reduced disease risk. This study examined associations between total and source-specific dietary protein intake and MetS reversion in Iranian adults. Adults with MetS at baseline (Phase 3, 2006–2008) of the Tehran Lipid and Glucose Study were followed until Phase 6. Dietary intake was assessed using a validated 168-item food frequency questionnaire. Total, animal and plant-based protein, as well as protein food-specific sources (red meat, processed meat, poultry, dairy, legumes, and nuts) was categorized into tertiles. MetS reversion was defined as the transition from MetS to non-MetS during follow-up, categorized by timing: final phase, any phase, early, and sustained reversion. Cox proportional hazards regression models estimated hazard ratios (HRs) and 95% confidence intervals (CIs), adjusted for covariates. In the fully adjusted models, participants in the second tertile of animal protein intake had a significant lower HR for “any phase MetS reversion” (HR: 0.68; 95% CI: 0.48–0.96), compared to the participants in the first tertile. Also, participants in the second tertile of poultry intake had higher HRs for “any phase MetS reversion” (HR: 1.47; 95% CI: 1.03–2.09) and “early phase MetS reversion” (HR: 1.58; 95% CI: 1.01–2.46), compared to the participants in the first tertile. Furthermore, higher intakes of dairy products and nuts were associated with 48% (HR: 0.52; 95% CI: 0.31–0.86) and 43% (HR: 0.57; 95% CI: 0.35–0.92) lower HRs for “early phase MetS reversion”, respectively. No significant associations were observed between dietary protein sources and sustained MetS reversion; however, the small number of sustained reversion events (<i>n</i> = 31, 5.4%) limited statistical power for this outcome, precluding definitive conclusions about long-term metabolic maintenance.</p>